J. Ky. Acad. Sci. 66(2):82-88. 2005. 



Cepaea nemoralis (Gastropoda, Helicidae): The Invited Invader 



Maggie Whitson 



Department of Biological Sciences, Northern Kentucky University, Highland Heights, Kentucky 41099 



ABSTRACT 



Marauding snails may not immediately come to mind when considering invasive species, but many non- 

 native snails have successfully colonized the U.S. The wood snail, Cepaea nemoralis (L.), is one of the most 

 striking of these introductions, due in part to its attractive shell coloration. This is one of the few snails that 

 people have purposely introduced into their gardens. Several populations are now established in Kentucky, 

 including a newly discovered population in Kenton County. The bright, striped or solid, yellow, pink, and 

 brown shells of this species have long caught the eyes of natural historians and biologists. Populations of 

 these snails are classic model systems for ecological genetics studies. While introduced populations of wood 

 snails seem to have had only minor impact as agricultural pests, they may have the potential to competitively 

 exclude some native species of snails. 



I 



INTRODUCTION 

 Though snails may not be the speediest of 

 beasts, several species have launched success- 

 ful invasions of the U.S. (Cowie and Robinson 

 2001; Dundee 1974; Mead 1971). Perhaps the 

 most glamorous of these invaders is the wood 

 snail, Cepaea nemoralis (L.). While many gas- 

 tropods rely on stealth and interstate shipping 

 to fuel their spread, wood snails have another 

 weapon in their arsenals: charm. Their color- 

 ful shells (see Figure 1) are nearly irresistible 

 to small children, nostalgic malacologists, and 

 many an evolutionary biologist. 



TAXONOMY 

 The wood snail belongs to the family Heli- 

 cidae, which includes the bulk of the Euro- 

 pean edible snails. It is a Linnaean species de- 

 scribed in 1758 and was originally Helix ne- 

 moralis, until Held established the genus Ce- 

 paea in 1837 (Abbott 1989). Currently four 

 species are included in the genus, of which C. 

 nemoralis is the type. The specific epithet 

 means 'of the woods' or 'inhabiting woods/ 

 groves' (Pilsbiy 1939; Reeve 1863; Rimmer 

 1907). 



Cepaea hortensis, the white-lipped grove 

 snail, is considered the sister species of C. ne- 

 moralis (Jones et al. 1977). Historically, tax- 

 onomists often treated C. hortensis as a variant 

 of C. nenwralis (Step 1901). The two species 

 are primarily differentiated by lip color of the 

 shells, which seems a minor feature in light of 

 the fact that C. nemoralis is the most variably 

 colored species in its genus and perhaps even 

 among European land snails. However, Rim- 



mer (1907) argued in support of recognizing 

 C. hortensis, having observed several mixed 

 populations and noting that of the many snails 

 seen paired on tree trunks, he saw no "mat- 

 rimonial alliances between these two forms." 

 Current taxonomists also take this view, and 

 the occasional hybrids produced by these spe- 

 cies are sterile (Jones et al. 1977). Both taxa 

 occur in the U.S., and though wood snails are 

 known to be introduced, there is disagreement 

 on whether C. hortensis is native or was also 

 introduced from Europe (Burch 1962; Dun- 

 dee 1974; Jones et al. 1977; Mead 1971). 



LIFE HISTORY AND NATIVE RANGE 



Native to central and western Europe, wood 

 snails are widespread in disturbed habitats, 

 from woodlands to fields and yards, but are 

 also found on chalk cliffs and even coastal 

 dunes (Reeve 1863). They are known by a va- 

 riety of common names, the Engfish ones in- 

 cluding banded grove snail, banded wood 

 snail, brown-lipped snail, and girdled snail 

 (Abbott 1989; Reed 1964; Step 1901; Turton 

 1857). This species has been widely intro- 

 duced and now has a nearly worldwide distri- 

 bution (Abbott 1989). 



Wood snails are obligately outcrossing her- 

 maphrodites, with both individuals exchanging 

 sperm during mating, and both individuals 

 able to lay eggs afterward (Stine 1989). Like 

 other members of the Helicidae, Cepaea snails 

 have a bizarre courtship behavior in which the 

 courting pair stabs each other with sharp, cal- 

 careous structures, aptly named darts, before 

 mating (Abbott 1989; Pilsbiy 1939). Wood 



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